Natural gas and L.P. gas are each frequently used in commercial and residential settings. Rather than having equipment that is limited in use to just one type of gas, it is desirable to have equipment that can be used with both types of gas, or at least which can be quickly and safely converted for use with each type of gas. Because natural gas and L.P. gas are typically delivered at different pressures, a number of attempts have been made to make a pressure regulator that is capable of operating in the different pressure ranges typical for the two types of gas. Examples of these attempts include Wolfehope, U.S. Pat. No. 3,128,086; Vicenzi et al., U.S. Pat. No. 3,451,421; Dykzeul et al., U.S. Pat. No. 3,338,264; Bauman U.S. Pat. No. 3,747,629; Murrell, U.S. Pat. No. 3,603,214; Gotthelf, U.S. Pat. No. 5,381,819; Buezis, U.S. Pat. No. 5,435,343. Most of these devices employ a diaphragm member for controlling a valve, and a spring which does not bias the diaphragm during operation at a first pressure, but which is manipulated in some way to engage and thus bias the diaphragm during operation at a second pressure. For example, in Bauman, U.S. Pat. No. 3,747,629, a conversion member is attached in one way so as not to engage a spring and is flipped over and attached another way so as to bias the spring. While of simple construction, this type of device presents the risk that the conversion member can be installed incorrectly.
The principal difficulties with the prior adjustable fluid flow regulators has either been the complexity of their construction and operation, or the risk that the regulator could be inadvertently switched from one mode of operation to the other, which poses the risk of appliance failure.